With the development of modern mobile communication and microwave communication as well as demands for high-performance, low-noise and low-cost radio frequency (RF) components, traditional silicon devices can no longer meet new requirements on technical specifications, output power and linearity. Therefore, SiGe HBT devices have been proposed which play an important role in the applications of high-frequency power amplifiers. Compared with gallium arsenide (GaAs) devices, though SiGe HBT devices are at a disadvantage in frequency performance, they can well solve the issue of heat dissipation accompanying with power amplification, benefiting from their better thermal conductivities and good mechanical capacities of their substrates. Moreover, SiGe HBT devices also have better linearity and higher integration level. Further, SiGe HBT devices are well compatible with the conventional silicon process and still belong to the silicon-based technology and the complementary metal oxide semiconductor (CMOS) process, thus reducing manufacturing cost. For these reasons, the SiGe BiCMOS (bipolar complementary metal oxide semiconductor) process provides great convenience for the integration of power amplifiers and logic control circuits.
Currently, SiGe HBT devices have been widely adopted internationally as high-frequency, high-power amplifier devices for wireless communication products such as power amplifiers and low-noise amplifiers used in mobile phones. In order to improve the output power of an RF power amplifier, it is an effective practice to increase its operating current or operating voltage within the normal operating ranges. Moreover, it is also important to reduce a SiGe HBT device's power consumption and improve its maximum oscillation frequency to reduce the resistance of its collector region through improvements in various kinds of process and device designs. Moreover, component miniaturization is also an important means to increase the integration level of integrated circuits, reduce some parasitic parameters (for example, base region resistance, collector region resistance, capacitances, etc.), and improve device performances.
Referring to FIG. 1, a SiGe HBT device of the prior art is fabricated according to the following steps: forming a buried layer 2 in a substrate 1; forming an epitaxial layer 3 on the buried layer 2; forming shallow trench isolations (STIs) 4 in the epitaxial layer 3; forming deep trench isolations (DTIs) 16 between the buried layer 2 and the substrate 1; forming a collector region 15 in the region located between the two inner STIs 4; implanting an impurity into the region between each of the two inner STIs 4 and an outer STI 4 adjacent thereto so as to form ion-implanted regions 5 on the buried layer 2; picking up electrodes of the collector region 15 through contact holes 7 formed on the ion-implanted regions 5; forming a base dielectric layer 14 on each of the two inner STIs, and forming a SiGe epitaxial layer in the region located between and on the base dielectric layers 14 to form a base region, which is composed of an intrinsic base region 12 and extrinsic base regions 9; and picking up electrodes of the base region through contact holes 7 formed on the extrinsic base regions 9.
In the above SiGe HBT of the prior art, the buried layer 2 and the ion-implanted regions 5 used to pick up the collector region will both increase the area of the device. Moreover, the practice of picking up the electrodes of the base region by using a bilateral symmetrical structure will also lead to the increase of the capacitance of the base-collector junction.